1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light [herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays, gamma-rays and the like.]
2. Description of the Prior Art
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photoconductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/Dark current (I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electro-photographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon in which dangling bonds are modified with mono-valent elements such as hydrogen or halogen atoms [hereinafter referred to as a-Si (H,X)] has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose their applications for use in image forming members for electrophotography, and German Laid-Open Patent Publication No. 2933411 its application for use in a photoconverting reading device. It is expected to be applied for electrophotography as an image forming member due to its excellent photoconductivity, friction resistance, heat resistance and relative easiness in forming into a large area device.
Generally, in production of an image forming member for electrophotography shaped in a drum having a photoconductive material comprising a-Si (H,X), for the purpose of obtaining good photoconductive characteristics, a-Si(H,X) film is formed on a drum-shaped substrate in a-Si(H,X) film depositing apparatus under the condition of heating the drumshaped substrate to a temperature of 200.degree. C. or higher.
However, because there is difference in coefficient of thermal expansion between the drum-shaped substrate and a-Si(H,X) film and also because of great internal stress within the a-Si(H,X) film, peel-off of the a-Si(H,X) film is frequently observed not only during deposition of the a-Si(H,X) film but also during cooling after deposition. Further, during usage as the photosensitive drum for electrophotography, a Si-(H,X) film may sometimes be peeled off by heating of the drum. In particular, a-Si film is susceptible to peel-off at the end portions of the drum, sometimes with formation of a crack from the end portion of the drum to the central portion.
According to a number of experiments by the present inventors, such film peel-off or crack formation is more liable to occur as the a-Si(H,X) film is thicker, and film peel-off may also be caused in the case of the a-Si type drum-shaped image forming member with a deformation of the drum-shaped substrate which will not cause film peel-off in the Se type drum-shaped image forming member for electrophotography of the prior art, for the above-mentioned reasons of difference in coefficient of thermal expansion and the greatness of the internal stress within the a-Si(H,X) film. As to the internal stress within the a-Si(H,X) film, it can be alleviated to some extent by selection of the production conditions of the a-Si(H,X) film (starting material gas, discharging power, heating temperature of the substrate). However, such film peel-off or crack formation is a critical defect when applied for electrophotography, which may be a cause for image defect
Generally speaking, the end portion of a drum is applied with a working for fixing the drum-shaped substrate within a manufacturing apparatus during production of a photoconductive member by deposition of a-Si(H,X) film or for fixing the drum-shaped photoconductive member for electrophotography in a copying machine. Since this working is generally practiced by cutting the inner face of the end portion, the end portion of the drum is thinner as compared with its central portion. Accordingly, heating of the drum-shaped substrate during forming a-Si(H,X) film is liable to cause thermal deformation particularly at its end portion, and this thermal deformation may be considered to be a cause for film peel-off or crack formation at the end portion of the drum. Also, such thermal deformation may be estimated to cause unevenness in discharging during deposition of a-Si film, whereby evenness in a thickness of the a-Si deposited film may be lost to give rise to an image defect.
The present invention has been accomplished in view of the various points as mentioned above. As the result of overall and extensive studies from viewpoint of applicability and utilization of a-Si for a photoconductive member to be used as an image forming member for electrophotography, solid state image pick-up device, reading device, etc., it has now been found that the above problem with respect to film peel-off and crack formation can be overcome by use of a drum-shaped substrate having a specific value of a ratio of the thickness of the end portion to that of the central portion as the support of a-Si deposited film. The present invention is based on such a finding.